The present invention relates to an electrical connecting device equipped in a steering column of a motor vehicle for electrically connecting an electric device mounted on the vehicle with an electric device mounted on a steering wheel.
An electrical connecting device for connecting an electric device mounted on a moving part with an electric device mounted on a stationary part usually employs a slip ring device. The slip ring operates to connect sliding contacts to keep electrical connection, and hence the connection may be influenced by dust and wetness, and/or vibration of the motor vehicle.
Accordingly, in recent years, the connecting device for an electric equipment which requires a particular reliability, such as an operating device for an air bag, uses a spiral flexible strip as disclosed in U.S. Pat. 3,525,536.
The electrical connecting device employed with the spiral flexible metal strip comprises an inner anchor ring secured to a steering shaft for a steering wheel to be rotated with the steering wheel and an outer anchor ring secured to a housing of a steering column. The flexible strip is loosely coiled in a spiral between the inner and outer anchor rings. An inner end portion of the flexible strip is electrically connected to the inner anchor ring and an outer end portion is electrically connected to the outer anchor ring. Upon rotation of the steering wheel, the slack in the loosely wound strip is either decreased or increased, depending on the direction of rotation of the steering wheel. If the inner ring is rotated with the steering wheel in excess of a permissible rotation angle with respect to the outer ring, an excessive load is exerted on the spiral flexible strip, which may cause the strip to break.
In order to resolve such a problem, the connecting device is attached to the steering wheel at a neutral position of the steering wheel where the inner ring is rotatable approximately by the same maximum angles in both the clockwise direction and the counterclockwise direction. To attach the connecting device at such a neutral position, the inner ring must be previously set to the neutral position of the steering wheel.
Heretofore, the inner ring is rotated to a maximum limit position in a direction and then returned a predetermined rotation in the opposite direction, so that the inner ring may set at a position near the neutral position. However, this manner lacks accuracy and the operation is troublesome.
Japanese Patent application Laid-Open No. 62-238164 discloses a neutral position indicating device for accurately positioning the inner ring at a neutral position. However, the neutral position indicating device comprises a number of parts. In addition, excessive load exerted on the flexible strip cannot be prevented.